Menstrual Phase: What's Happening During Your Period

The menstrual phase is the bleeding portion of your cycle — days 1 to 5 in a typical 28-day cycle. It’s the hormonal floor of the month: estrogen and progesterone are at their lowest, the uterine lining is shedding, and the body is in a brief recovery and reset window before the follicular phase rebuilds.

This guide covers what’s actually happening during your period, what’s normal, what’s worth investigating, and how to support your body through it.

Quick facts

• When: Day 1 of bleeding to roughly day 5 (varies — 3–7 days is normal)
• Defining hormones: Lowest levels of estrogen and progesterone in the cycle
• What’s happening: The corpus luteum has degraded; without hormonal support, the endometrium sheds
• Total blood loss: 30–80 mL across the period (about 2–4 tablespoons)
• How most women feel: Low energy days 1–2, gradually recovering through days 3–5

What causes menstrual bleeding

If pregnancy doesn’t occur, the corpus luteum — the temporary structure that produced progesterone during the luteal phase — degenerates around day 24–26 of the cycle. Progesterone and estrogen drop sharply.

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Without those hormones keeping the endometrium stable, the lining starts to break down. Blood vessels in the uterine wall constrict, then relax, then constrict again — and the lining sheds in pieces, mixed with blood and uterine fluid. The whole process is driven by prostaglandins, the same compounds responsible for menstrual cramps.

The bleeding lasts as long as the lining takes to fully shed. Most women lose about 30–80 mL of blood across the whole period — far less than it often feels like.

Why day 1 of your period is “day 1” of your cycle

Cycle counting starts on the first day of full bleeding for two reasons:

1. It’s the most consistently observable event — the start of bleeding is unambiguous, unlike ovulation or the end of menstruation
2. It marks the hormonal floor — every cycle begins from the same low-estrogen, low-progesterone baseline

The menstrual phase overlaps with the start of the follicular phase. While the lining is shedding, FSH is already starting to rise and new follicles are beginning to develop. By day 5–6, the period is winding down and the follicular phase is firmly underway.

For the broader cycle structure, see menstrual cycle phases.

Suggested read: Cycle Syncing Exercise: Evidence vs. Hype

What’s typical during your period

Days 1–2

This is the heaviest stretch for most women. Common experiences:

• Cramps — usually peak on day 1, often worst the first 24 hours
• Fatigue, lower energy, lower motivation
• Lower mood for some women — usually mild
• Possible headache or back pain
• Slightly higher hunger for many

Days 3–5

Bleeding tapers. Symptoms usually improve.

• Energy starts climbing
• Cramps usually gone by day 3
• Mood lifting
• Skin sometimes feels flat or dry due to low estrogen

Day 5–7

Period ends. Estrogen is climbing. Most women feel a noticeable lift in energy and mood from here through ovulation.

Period cramps: what’s actually happening

Cramps (dysmenorrhea) are caused by uterine contractions driven by prostaglandins — fatty acid compounds produced in the uterine lining. Higher prostaglandin levels = stronger contractions = more cramping.

What helps:

• NSAIDs (ibuprofen, naproxen) are first-line. They work by inhibiting prostaglandin synthesis — so they’re attacking the root cause, not just the pain. Take at the first sign of cramps; they’re more effective when started early.
• Heat — a heating pad on the lower abdomen reduces cramp severity for most women. Evidence supports it as effectively as some OTC pain relievers.
• Magnesium — relaxes smooth muscle. Best to take continuously, not just during the period. See magnesium for PMS for dose and form details.
• Herbal teas — ginger, chamomile, and peppermint have modest evidence. See tea for menstrual cramps for specifics.
• Movement — light walking, stretching, and yoga reduce cramps for many women, even though it can feel counterintuitive. A structured hip flexibility routine targets the muscle groups most involved.
• Foods — anti-inflammatory diet, omega-3, magnesium-rich foods. See foods that help with muscle cramps.

If your cramps are severe enough that NSAIDs don’t help, you can’t function, or they’ve changed in character, see a doctor. Severe period pain is the main symptom of endometriosis, which is dramatically underdiagnosed.

Suggested read: Perimenopause: Symptoms, Duration, and Treatment Guide

Energy and training during your period

Days 1–2 are the genuinely lower-energy stretch of the cycle. A 2020 systematic review of 78 studies on exercise performance and menstrual cycle phase found that performance was slightly reduced in the early follicular phase (the first few days of bleeding) compared to all other phases.¹

A separate meta-analysis on exercise-induced muscle damage found that DOMS and strength loss were higher in the early follicular phase, when sex hormones are at their lowest.² So intense training in the first 2–3 days of your period may genuinely hurt more and recover slower.

Practical approach:

• Days 1–2: Light to moderate movement. Walking, gentle yoga, mobility work. Avoid PR attempts and high-volume strength training.
• Days 3–5: As bleeding tapers, training can return to normal. By day 4–5 most women feel back to baseline.
• Cardio is usually fine — it’s the high-intensity and heavy strength work where the early-period dip shows up most.

Iron and your period

Each period averages 30–80 mL of blood loss, which means losing 15–40 mg of iron per cycle. Over a year, that’s 180–480 mg — significant.

Women with heavy periods are at real risk for iron deficiency, which causes:

• Fatigue out of proportion to sleep
• Brain fog and poor concentration
• Hair shedding
• Pale skin, brittle nails
• Reduced exercise capacity

If any of those sound familiar, see iron deficiency symptoms and consider getting a ferritin test. Dietary support: see high-iron foods and iron-rich plant foods for the food piece, and ways to increase iron absorption for getting more out of what you eat.

Whether to supplement depends on your bloodwork — see should you take iron supplements for the honest answer.

Skin and mood during your period

Skin: Low estrogen during the menstrual phase means lower sebum production, less skin hydration, and a flatter, sometimes dry appearance. The good news is that hormonal acne — which is usually a luteal phenomenon — typically resolves by day 3 or 4.

Mood: For most women, the menstrual phase mood is better than the late luteal phase. The drop in progesterone and the start of estrogen recovery often produces a noticeable mood lift on day 2 or 3. If your mood stays low or gets worse during your period, that’s a flag — it could indicate underlying depression, iron deficiency, or another issue.

Suggested read: How Long Does Perimenopause Last? Phases and Timeline

What’s normal vs. worth investigating

Bring up with a doctor:

• Periods that prevent you from functioning normally
• Bleeding between periods
• Very heavy periods (especially with fatigue or breathlessness — could be anemia)
• Skipped periods if you’re not on birth control
• Sudden changes in pattern after years of consistency
• Severe pain — possible endometriosis, fibroids, or adenomyosis

What to do during your period (practical)

A simple framework for the bleeding days:

Days 1–2:

• Sleep slightly more if you can — your body is doing real work
• Lighter movement, not full rest unless you genuinely need it
• Take NSAIDs early for cramps if you use them
• Hydrate well — fluid retention and bleeding both increase water needs
• Iron-rich foods if your periods are heavy

Days 3–5:

• Return to normal activity as bleeding tapers
• Energy will climb naturally
• A good window to plan for the higher-energy follicular phase coming up

What’s coming next

As your period ends, FSH rises, follicles start developing, and estrogen begins climbing. The next two weeks — the follicular phase into ovulation — tend to be the highest-energy stretch of your cycle. Then the luteal phase takes over, and the cycle starts again.

Bottom line

The menstrual phase is the bleeding, low-hormone reset window of your cycle. Days 1–2 are genuinely lower-energy; days 3–5 are recovery. Manage cramps with NSAIDs taken early, heat, and magnesium. Train lighter the first two days but don’t stop moving entirely. Pay attention to iron if your periods are heavy. Anything beyond normal flow, length, or pain deserves a doctor’s input — not because it’s necessarily serious, but because problems show up here first and are dramatically underdiagnosed.